...oh yeah and...
...you can also use Skype through any 3G bluetooth mobile phone.
I don't know why Nokia keeps pushing the wifi angle, most of the time the mobile connection is the most convenient to use as mobile networks have much better coverage than wifi. They're not that expensive to use for data any more if you have an unlimited net access agreement with your network.
The reason why Nokia is going to be pushing Wifi over 3G is mainly to do with reliability, while 3G is ever growing an with HSDPA coming in things are getting better however with the data speeds you can get through Wifi using Skype should normally give you a service comparable to regular phone call, with 3G and when your on the move in particular the fluctuating 3G signal is going to vary the quality of the call you get..
On a side note, not all networks are permitting the use of such applications and are actually blocking the data ports necessary for them to function..